Clinical trials have helped clarify the efficacy of clopidogrel for the treatment and prevention of vascular disease. Costs for its use exceeded $5.9 billion in 2005, making it the second greatest source of drug expenditure in the world. However, little is known about the appropriateness of that use. Overuse of clopidogrel could have important implications for health care quality and drug expenditures.

We conducted a retrospective cohort study linking all filled prescriptions to all clinical encounter data for Medicare beneficiaries enrolled in a large state-wide pharmacy assistance program. We identified all patients newly prescribed clopidogrel during a recent 2-year period and determined the proportion who had indications for clopidogrel, the mean number of tablets filled by patients with and without apparent indications in the year after starting therapy, and the costs associated with the observed patterns of clopidogrel use.

We identified 4977 patients who were newly prescribed clopidogrel. Of these patients, only 47% had ≥1 documented indications for clopidogrel according to clinical trial findings. Using looser criteria, the number of patients with appropriate indications was 56%. During the first year of therapy, 43% ($2.05 million) of total clopidogrel expenditures for the patients studied was spent on patients without an indication that this agent was required, using the extended criteria for evidence-based use.

More than 40% of the clopidogrel used in this population appears to have been prescribed to patients for whom the drug had no documented advantage over aspirin or no antiplatelet therapy. If the same proportion applies nationally, in 2005, it would represent almost $1.5 billion of potentially unnecessary health care expenditure.